Effects of Fragmentation and Hybridization on Geographical
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Received Date : 02-Sep-2015 Revised Date : 19-Apr-2016 Accepted Date : 15-May-2016 Article type : Original Paper Editor : Ian Hartley Running head: Song variation in the endangered Yellow Cardinal Effects of fragmentation and hybridization on geographical patterns of song variation in the endangered Yellow Cardinal Gubernatrix cristata MARISOL DOMÍNGUEZ*, JUAN CARLOS REBOREDA & BETTINA MAHLER Article IEGEBA-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160, Ciudad Universitaria, C1428EGA, Buenos Aires, Argentina *Corresponding author. Email: [email protected] The song learning process may lead to small-scale geographical variation in vocalizations of oscine birds. This variation can be further enhanced by the effects of habitat fragmentation or hybridization. Populations of the endangered Yellow Cardinal Gubernatrix cristata are now patchily distributed in the southern South American thorny shrubland forests and are small as a consequence of the pressure exerted by increased habitat transformation and illegal trade. This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as Accepted doi: 10.1111/ibi.12388 This article is protected by copyright. All rights reserved. We study the Yellow Cardinal’s vocalizations throughout its distribution and assess how habitat characteristics and fragmentation, as well as hybridization with the Common Diuca Diuca diuca, have affected song patterns of different populations. We expected to find song differences among populations and songs to be more similar to those of the Common Diuca in areas where hybridization occurs. Multivariate analyses revealed significant differences in song between the four populations studied and confirmed that songs are more similar to those of Common Diuca where hybridization takes place. These results, in conjunction with genetic studies, can help to establish management units that preserve genetic and cultural variation in this endangered species. Article Keywords: cultural units, oscines, vocalizations, hybrids The song of passerine birds is a conspicuous display shaped mostly by sexual selection in the context of male-male competition or mate attraction (Catchpole & Slater 2008) and is an essential trait in social interactions of birds (Odom et al. 2014). Songbirds acquire their specific song patterns by social learning and this is probably one of the best studied examples of a cultural trait in non-human animals (Slater 1986). This non-genetic transmission of vocal traits across generations can be a powerful source of variation due to copying inaccuracies (Dawkins 1976, Mundinger 1980, Lynch 1996). Imitative vocal learning enables the ready generation and rapid transmission of novel patterns of vocal structure (Slater 1989, Slabbekoorn & Smith 2002) leading to differences in song among individuals and among populations of the same species (Catchpole & Slater 2008). Geographical variation in bird songs evolves through the dynamic interplay of song learning mechanisms and isolation and is influenced by the effects of dispersal behaviour, Accepted cultural drift, genetic drift, cultural selection, natural selection and sexual selection (Podos et This article is protected by copyright. All rights reserved. al. 2004, Podos & Warren 2007). Cultural drift can lead to the random fixation of a few song types or note types in isolated populations (Lynch & Baker 1994, Grant & Grant 1996, Baker et al. 2001, Koetz et al. 2007) over short evolutionary timescales (Baker et al. 2003, Edwards et al. 2005). This process is important in conservation biology as large contiguous populations become increasingly reduced to small isolated populations through habitat loss and fragmentation, potentially having an impact on culturally transmitted traits (Laiolo & Tella 2007, Caro & Sherman 2012, Jamieson & Lacy 2012). Bird songs, in particular, become impoverished as a result of disruption of cultural transmission (Laiolo & Tella 2005, 2006, Parker et al. 2010, 2012). Incorporating the study of cultural attributes in a conservation context has been Article recently suggested as a novel aspect of the diversity and status of animal populations (Slabbekoorn & Smith 2002, Laiolo & Jovani 2007, Wildermuth et al. 2013). It has been proposed that animal culture should be integrated into conservation biology (Whitehead et al. 2004) and that ‘culturally significant units’ should be preserved in small and endangered populations (Ryan 2006). The songs of small populations isolated by habitat fragmentation have been shown to correlate with population viability (Laiolo 2008, Laiolo et al. 2008), with smaller populations, that are more susceptible to extinction, presenting lower variability in their songs. In the context of rapid landscape change and deep concern about diversity loss, understanding how landscape fragmentation affects and structures natural populations is important for improving ecological knowledge and defining optimum strategies for conserving threatened species (Pearman &Wilbur 1990, Diniz-Filho & Telles 2002, Manel et al. 2003). We analyze the geographical song variation of the Yellow Cardinal Gubernatrix cristata (Thraupidae), a passerine endemic to southern South America, which at present is Accepted This article is protected by copyright. All rights reserved. categorized by IUCN as Endangered (BirdLife International 2016). In the past, this species was widely distributed in the thorny deciduous shrubland forests of central Argentina (Espinal region), most of Uruguay and parts of southern Brazil (Ridgely & Tudor 1994; Fig. 1). However, for over a century there has been a continuous removal of individuals, mainly males, to commercialize them as cage birds (Pessino & Tittarelli 2006, BirdLife International 2016). This, in addition to the conversion of their forest habitat to agriculture and cattle pasture, has caused a marked decline in range and population size. Now the species’ distribution is discontinuous, with the main populations found at the extremes of the original range (Collar et al. 1992, BirdLife International 2016; Fig. 1). In Brazil, Yellow Cardinals are now very rare (Fontana et al. 2003, Machado et al. 2008). Article A further consequence of rarity is that hybrids of Yellow Cardinals with the Common Diuca Diuca diuca minor have been found in the southern part of the Cardinal’s range, probably as a consequence of the lack of Cardinal males due to illegal trade (Bertonatti & López-Guerra 2007). We therefore analyzed Yellow Cardinal vocalizations throughout the species’ range and assessed how habitat characteristics and fragmentation, as well as hybridization with the Common Diuca, affected song patterns of different populations. We expected to find song differences among populations because, in the presence of natural selection shaping vocalizations, songs should show features that are better transmitted in each particular environment (Morton 1975). If song geographical variation is a consequence of cultural drift we expect to find random loss of vocal variants in different populations, that is then intensified by habitat fragmentation. We also expected to find songs more similar to those of the Common Diuca in areas where hybridization occurs. Accepted This article is protected by copyright. All rights reserved. METHODS Song recordings Recordings were obtained during four breeding seasons (September –January 2011–2014) in four different populations covering most of the known distribution of the Yellow Cardinal in Argentina and Uruguay: 1) Corrientes (C); 2) San Luis (SL); Rio Negro (RN); and 4) Uruguay (U; Fig. 1). The possibility of repeated recording of the same male was minimal since most birds were previously ringed. The songs of Common Diucas were recorded in the southern part of the Yellow Cardinal’s distribution (La Pampa and Rio Negro provinces) where hybridization events have been registered (Bertonatti & López Guerra 1997; Fig. 1). Songs of Diucas from other areas (n = 3) were obtained from the Cornell Lab of Article Ornithology’s Macaulay Library collection (catalog numbers 135815, 20607 and 20605). All recordings were made within close proximity to singing birds (5–10 m) using a Zoom ZOH4NK H4n Handy Recorder. The dataset included 3–8 high quality songs per individual of 30 Yellow Cardinal males and 18 Common Diucas. Some songs were discarded because of poor recording quality but a total of 245 songs were analyzed. We digitalized songs with the Sound Analysis software package “RavenPro” version 1.4 (Charif et al. 2007) and visualized spectrograms with a ‘Hamming’ window type, a frame size of 256 samples, and a bandwidth of 224 Hz. For the colour scheme we chose the ‘grayscale’ option, and brightness and contrast values were set at 50% in all cases to standardize the measurements. Song analysis Songs were characterized as a series of elements (notes) emitted successively with short intervals and followed by an interval of silence longer than the song. A note was defined as any continuous trace in the temporal axis of the spectrogram. We identified different note Accepted This article is protected by copyright. All rights reserved. types in Yellow Cardinal songs which were visually classified on the basis of ascending or descending frequency modulations (Fig. 2). On each